The present invention relates to a data transmission and display system. More particularly, the present invention relates to a data transmission and dislay system in which data is transmitted synchronously in a first direction by an output data source to a display device and associated input/output devices, and data originating from an input/output device is transmitted asynchronously in the reverse direction to the input data source, the bi-directional transmission taking place over a common data transmission line. The invention also relates to apparatus for achieving the display by the display device of images of data characters having one or more display attributes or characteristics.
Various data transmission and display systems have been constructed and proposed heretofore in which display data originating from an input data source (e.g., a data processor) is transmitted over a suitable data transmission line, such as a coaxial cable transmission line, to be displayed by a remote display device such as a video display monitor. While such systems operate in a generally satisfactory manner, the coaxial cable transmission lines used therein are ordinarily not employed to carry other types of data, specifically, control data to be used to address and control one or more input/output devices (e.g., a keyboard or a light pen) associated with the display device or to carry data originating from one of the input/output devices back to the input data source to be processed thereby. Rather, in systems of the above type, other kinds of transmission lines such as twisted pairs are used to accomplish the abovementioned additional functions. These other kinds of transmission lines generally add to the costs of the system and, in addition, require additional circuitry which also adds to the costs of the system. Further, the transmission of data in systems of the above type is often synchronous in both directions and therefore requires the extensive use of synchronization data and related circuitry to achieve the synchronous formatting of the data.
Data transmission and display systems of the above type also generally are limited as to their display capabilities. In many of these systems characters may be displayed by a display device so as to be intensified, inverted (black on white instead of white on black), underlined, to be light pen detectable, or to have a width greater than a predetermined normal width. However, these systems generally lack the capability or versatility of displaying characters to have simultaneously several of the abovementioned display attributes, and possibly others, and, also, in the particular case of displaying characters of different widths, to display characters of one width and characters of a different width in the same character row of the display device. In addition, these systems generally lack circuitry capable of using attribute data to cause images of data characters to be displayed in one row of a display device with particular display attributes specified thereby and, using the same attribute data, to cause images of data characters to wrap-around to a new display row of the display device to be displayed therein with the same display attributes.